This invention relates to an improved circuit arrangement for actuating a warning device in response to abnormal conditions of a vehicle hydraulic brake system with main and auxiliary sources of hydraulic pressure.
In vehicles equipped with hydraulically-actuated power brake boosters, an engine-driven or main source of hydraulic pressure, such as a power steering pump, may be utilized in combination with a auxiliary source of hydraulic pressure, such as a second pump driven by an electric motor powered off the vehicle battery. When the vehicle and its brake system are operating normally, the power steering pump operates when the vehicle engine is operating.
One prior art electronic brake system warning circuit generates a warning signal in response to various abnormal conditions of such a brake system. Particularly, an abnormal condition exists when the ignition switch is "on", but the main pump is not operating. However, the referenced warning circuit does not generate a warning signal in response to this abnormal condition, unless simultaneously with this condition, there also occurs either (1) an operator brake application, or (2) an open circuit condition in the auxiliary pump motor.
Another warning circuit is described in copending application Ser. No. 83,443, which is commonly assigned with the present application. Neither of these warning circuits energizes the auxiliary pump when the main pump is not operating while the vehicle ignition is on in the absence of an operator brake application. Therefore, an undesirable time lag between brake application and the generation of full reserve brake pressure could result since the auxiliary pump is not actuated until the brakes are applied. Furthermore, with neither of the circuits described above, can a vehicle operator discriminate among any of the particular conditions under which warning signals are generated.
A third warning circuit is described in copending application Ser. No. 83,441, which is commonly assigned with the present application. However, this third circuit only generates a warning signal in response to the blowing of a fuse which is used to protect brake system control circuitry.